Is a leaning tree always dangerous?
Often people assume that a leaning tree poses a danger to the safety of their house or family and therefore the tree needs be removed.
Trees don’t always grow perfectly upright. In fact, a lean can be completely normal for that tree. Some species develop a lean as they compete for sunlight, especially in sheltered gullies or dense gardens. Others may have established on a slope and grown at an angle from a young age. Coastal winds around Auckland can also influence a tree’s growth habit over time, shaping it gradually rather than causing structural failure.
So how do you tell the difference between a stable lean and a hazardous one?
There are a few key things we look for when making an assessment of a leaning tree and its stability and safety, or the probability of failure.
They include evidence of bark compression and tension. Does one side of the tree have rougher bark than the other, which may be much smoother by comparison? This occurs as the bark is stretched on one side and bunched on the other, indicating that the tree is responding over time to slow and gradual forces in the direction of lean.
Trees that have leaned slowly over time often develop a natural curve near the base as they correct their growth. This adaptive growth, known as reaction wood, is a strong indicator the tree has stabilised itself. A straight trunk that has suddenly shifted, however, suggests recent movement and potential instability
Are the roots showing cellular changes for added strengthening? A tree that has been leaning for some time, often for many years, may respond by laying down strengthening cells to stabilise the tree. This could indicate the tree is coping well with the lean. It’s a bit like laying down muscle for a bodybuilder when they do loads of upper-body strength training; it doesn’t happen overnight but requires consistent growth over a long period of time.
Is there evidence of ground heave? If the earth around the tree begins to lift, it is a sure sign that the tree may be unstable and is not coping with the lean. This often happens in unusually strong winds and storms esp. where the earth is waterlogged. Look at the soil around the base. Fresh soil cracking, lifting, or heaving on one side of the trunk can indicate recent root plate movement — a clear warning sign. Exposed or broken roots are also cause for concern. By contrast, a stable leaning tree will usually show no recent soil disturbance. The ground will be firm, and the roots well-anchored.
Is the lean a result of phototropic growth, (towards light)? A tree that has naturally grown on a lean to access light needed for photosynthesis may have made provision in the roots for this type of growth. Although not necessarily dangerous, this type of growth and the stability can be compromised as the tree gets bigger and limbs get heavier.
Canopy health also matters. A tree with full foliage, good leaf colour, and no significant dieback is generally functioning well. Decline in the canopy combined with a new lean may signal root damage or disease.
At The Treeman, we always recommend assessment before action. Removing a mature tree unnecessarily not only reduces shade and habitat but can also impact soil stability and property value. A professional arborist can determine whether a leaning tree is adapting successfully or showing signs of structural failure.
If there are concerns that the tree is not coping structurally, then an arborist can remove some of the weight on a leaning side to reduce the load on strategic limbs.
Leaning doesn’t automatically mean dangerous. Sometimes, it simply means the tree has grown to suit its environment — and is doing just fine.
As experienced Arborists with International Tree Risk Assessment Qualifications (TRAQ), we can advise you on how safe your tree is by using a matrix system to assess a probable or possible outcome. This means you can make an informed decision on the fate of your leaning tree.